Beef Cattle Browsing
Editor: Dr. Stephen Hammack, Professor & Extension Beef Cattle Specialist Emeritus
August 2007
This newsletter is published by Texas AgriLife Extension – Animal Science. Media, feel free to use this information as needed and cite Texas A&M University Beef Cattle Browsing Newsletter, Dr. Steve Hammack.
PROGRAMS FOR HEIFER DEVELOPMENT
USDA-Miles City, Montana researchers studied three systems for developing replacement heifers. Early February- and early April-born heifers were weaned at either 190 or 240 days of age. Late May-born heifers were weaned at either 140 or 190 days. Half of each group was then developed on a constant gain program on corn silage and hay until breeding at approximately 14 months of age. The other half was developed for delayed gain on pasture, with hay and supplement as needed, until three months before breeding. At that time the older delayed heifers were fed corn silage/barley in drylot and the younger heifers were moved to spring range grazing. The development program did not affect body weight at breeding. Early-born and later-weaned heifers were heavier at breeding. There was no difference in luteal activity or pregnancy rates among any of the groups. The authors concluded that producers have considerable flexibility in developing heifers without adverse effects on reproductive performance. (J. Animal Sci. 85:2048)
DO MISSED MEALS HURT PERFORMANCE
Species other than cattle are usually not considered here. However, some recent pig research may be of interest. Kansas State University researchers withheld feed from growing pigs to simulate “out-of-feed events” such as late feed delivery or bridging in feed delivery systems. In two studies over 35 days and 85 days some pigs were out of feed for 20 hours. Various combinations of timing and number of out-of-feed events were included in the studies. These combinations ranged from some treatments having feed withdrawn only once while in others there was withdrawal every week at random times. There were no significant differences in total gain among the groups. (J. Animal Sci. 85:2043)
GENDER & GENETIC EFFECTS ON ENERGY & PROTEIN REQUIREMENTS
Texas A&M and Brazilian researchers studied energy requirements in cattle out of Nellore dams and the same Red Angus sire. The study was conducted in Brazil. Over 84 days, cattle were fed for maintenance or to achieve two levels of weight gain. Net energy and protein required for maintenance did not differ among bulls, steers, and heifers. Also, protein required for growth did not differ. However, energy required for growth was lower for bulls. The authors also concluded that “the energy requirement of crossbred Bos indicus x Bos taurus for maintenance might be less than that of purebred Bos taurus.” (J. Animal Sci. 85:1971)
EFFECTS OF SICKNESS IN THE FEEDLOT
Texas A&M Ranch to Rail documented the ill effects of sickness on feedlot performance and carcass merit. In a recent report, New Mexico State and Texas A&M collaborated in New Mexico Ranch to Rail which provided additional evidence. From 2000 to 2003, over 800 steers were fed. Classification was made as follows: healthy, never treated (NT); one medical treatment (1T); two or more treatments (2T). Distribution was 78% NT, 17% 1T, and 5% 2T. Initial weight did not differ, so that factor did not affect sickness. NT gained 0.18 lb/day more than 1T which gained 0.26 lb/day more than 2T. As ADG increased, days on feed decreased. Unlike the earlier Texas A&M Ranch to Rail data, there were no significant differences in any carcass factors. Death loss was 0.3% for NT, 3.6% for 1T, and 8.0% for 2T. Also, less than 1% of both NT and 1T were marketed early as “railers”, compared to 13.2% for 2T. Gross income for NT was $28.52 higher than 1T, which was almost exactly accounted for by the average medicine cost of $28.43 for 1T. Gross income for 1T was $144.15 higher than 2T, which had additional medicine cost of $34.20 over 1T. (Prof. Anim. Sci. 23:174)
EFFECTS OF IMPLANTS ON CARCASS & PALATABILITY TRAITS
Colorado State University researchers studied 500 British x Continental heifers obtained from the same backgrounding operation. Experimental groups were first stratified into heavy and light groups (divided at 750 lb) within which there were non-implanted controls, one initial implant, or two implants (re-implanted 85 days before projected slaughter). This resulted in treatment groups receiving over the feeding period various totals of trenbelone acetate (TBA, from 0 to 400 mg total) and/or estradiol (ED, from 0 to 40 mg total). Initially heavier groups were slaughtered after 135 days on feed, and lighter groups at 149 days.
One implant increased carcass weight 17 lb over controls without affecting marbling, quality grade, or tenderness. A second implant increased carcass weight 13 lb over one implant but also lowered percent grading Choice or Prime and reduced tenderness. Tenderness decreased linearly as the total level of TBA and ED increased. Also, TBA/ED combination implants, compared to TBA only, resulted in larger ribeyes, lower marbling, and lower tenderness. Longer postmortem aging (21 to 28 days) diminished adverse implant effects on tenderness. There were definitely tradeoffs between rate of gain/muscling and carcass/palatability factors. Carcass aging appeared to mitigate effects of implanting and improve tenderness whether or not implanting was used. (J. Animal Sci. 85:2019)
BOVINE RESPIRATORY DISEASE (BRD) vs. FEEDLOT & CARCASS TRAITS
Researchers at the U. S. Meat Animal Research Center (Clay Center, NB) analyzed records from over 18,000 cattle collected over 15 years. The estimated heritability of BRD incidence was very low at 0.08. (Heritability of ADG, marbling, percent retail product, and tenderness ranged from 0.31 to 0.63). Genetic correlations between BRD and other factors were low (below 0.2). The only exception was an estimate of -0.42 between BRD and percent bone in the carcass, indicating that cattle with more bone would tend to have lower incidence of BRD. So, response to genetic selection for reduced BRD incidence would probably be extremely slow at best. On the other hand, selection for improved feedlot performance and carcass merit should have little if any effect on the incidence of BRD. (J. Animal Sci. 85:1885)
COMPARISONS OF TIMED-AI PROGRAMS FOR COWS & HEIFERS
University of Missouri researchers compared two programs for timed-AI breeding of 650 cows, averaging mid-5 Body Condition Score, at four locations. The MGA Select program involved: feeding MGA for 14 days, injection of gonadotrophin-releasing hormome (GnRH) on day 26, injection of prostaglandin (PG) on day 33, and mass AI 72 hours later. The CO-Synch + controlled internal drug release (CIDR) program involved: feeding non-MGA carrier for 14 days, GnRH injection and insertion of a CIDR containing progesterone on day 26, CIDR removal and PG injection on day 33, and mass AI 66 hours later. There was no significant difference in pregnancy rate between the two programs.
Two programs were compared using 217 heifers at three locations. CIDR Select involved: insertion of a CIDR for 14 days, injection of GnRH on day 23, injection of PG on day 30, and timed AI 72 hours later. CO-Synch + CIDR involved: GnRh injection and CIDR insertion on day 23, CIDR removal and PG injection on day 30, and timed AI 54 hours later. At one location, estrous response was greater and variation was reduced for interval to estrus after PG with the CIDR Select program. Over all locations, CIDR Select resulted in significantly greater pregnancy rates, 62% versus 47% for CO-Synch + CIDR. (J. Animal Sci. 85:1933 and 1940)